Recently, boron nitride (BN) films have found increasing application in semiconductor devices. For example, boron nitride films have been recognized as useful for dielectric isolation in integrated circuits where excessive signal propagation delay is caused by stray capacitance between adjacent electrically conductive leads. Boron nitride has a low dielectric constant relative to other commonly used insulators, such as silicon nitride and silicon dioxide. In addition, boron nitride exhibits high hardness. The high hardness of a boron nitride film enables it to be used as a polish-stop layer for a polish planarization process.
Although BN possesses many desirable characteristics, under certain conditions it can absorb moisture, which changes its physical and electrical properties. Additionally, unless care is taken during the deposition process to insure that a specific microstructure is formed, the BN film is somewhat brittle. In an effort to further enhance the utility of BN as a dielectric material, and to increase the toughness of BN, silicon has been added to boron nitride to form silicon boron nitride (SiBN). The addition of silicon to BN increase the durability and reduces water absorption characteristics of the film by stabilizing the microstructure of the BN during deposition. The actual structure of the film is a composite of silicon nitride and boron nitride. The low dielectric constant and film durability makes SiBN a useful interlevel dielectric material.
While the addition of silicon to BN yields improved film characteristics, advanced VLSI integrated circuits require dielectric films having even lower dielectric constants than that provided by SiBN. To further reduce the dielectric constant of SiBN, oxygen can be added to the SiBN film. An oxygen-doped SiBN film has a lower dielectric constant than undoped SiBN. Although a reduction in the dielectric constant is obtained with the addition of silicon to a BN film and a further reduction is observed with the addition of oxygen to SiBN, the addition of many elements makes the film deposition process more complex. For example, for each additional element, a source must be provided and a new set of optimum deposition conditions must be ascertained. Moreover, as the number of elements in the film increases, the control of the microstructure during film deposition becomes more difficult. In view of the advantages inherent in the use of BN as a thin-film in semiconductor devices, further development work is necessary to provide a high-quality BN film and deposition method.